The MPA booster series have an RJ45 input for connection to MBT 1101 pre-amplified microphone bases simply by means of SFTP CAT.5E shielded cables. There is a special balanced input (TEL/EMERG) with a transformer and automatic activation of precedence (VOX) on the rear panel. Controls for adjusting the level and activation threshold are present on the rear panel. This input can be used for connecting the appropriate audio output of a telephone switchboard. This equipment has a large number of devices for protection against overloads and short circuits (an output current peak-limiting circuit, a thermal circuit-breaker inside the power transformer, a resettable thermal circuit-breaker in contact with the power-transistor heat sink, main fuses). In addition, each unit has a cooling fan, with automatic control of the spped depending on the temepratures of the heat sinks to which the power devices are applied.